Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09G—POLISHING COMPOSITIONS; SKI WAXES
  • C09G1/00—Polishing compositions
  • C09G1/02—Polishing compositions containing abrasives or grinding agents
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/14—Anti-slip materials; Abrasives
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/14—Anti-slip materials; Abrasives
  • C09K3/1409—Abrasive particles per se
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/14—Anti-slip materials; Abrasives
  • C09K3/1454—Abrasive powders, suspensions and pastes for polishing
  • C09K3/1463—Aqueous liquid suspensions

Definitions

• the present invention relates to a polishing composition using silica-based abrasive grains and a method for producing the same.
• a polishing composition using silica-based abrasive grains is used for polishing silicon wafers.
• the polishing composition generally contains silica-based abrasive grains in an aqueous medium such as water, and further contains an alkaline compound, a water-soluble compound, a chelating agent, an oxidizing agent, a metal corrosion inhibitor, and the like.
• a polishing composition has been disclosed that is defined using a function indicating affinity with water, which is calculated from the relationship between the inverse of the relaxation time of pulse NMR in a dispersed state of silica abrasive grains and the total surface area of the silica abrasive grains (see Patent Document 1).
• polishing composition has been disclosed in which the relationship between the BET specific surface area of silica particles contained as abrasive grains and the specific surface area measured by a pulsed NMR method is defined (see Patent Document 2). Furthermore, polishing compositions have been disclosed in which the NMR relaxation time is evaluated using the solvent affinity of abrasive grains (see Patent Documents 3 and 4).
• An object of the present invention is to provide a polishing composition which achieves a high removal rate when used for polishing silicon wafers and has improved storage stability during storage or transportation.
• the inventors focused on the amount of water molecules bound to the surface of silica particles, using the Rsp value derived from the relaxation time obtained by pulse NMR measurement as an indicator, and discovered that by using silica particles having an Rsp value within a predetermined range as abrasive grains, the storage stability of the polishing composition can be improved while maintaining high polishing performance.
• the polishing composition according to the first aspect in which the silica particles have an average secondary particle diameter of 40 to 200 nm measured by a dynamic light scattering method and an average primary particle diameter of 20 to 100 nm measured by a nitrogen gas adsorption method.
• the polishing composition according to the first aspect wherein a treatment liquid obtained by contacting the silica particle aqueous dispersion with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is frozen at ⁇ 70° C.
• the treatment liquid is further freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersion medium, to obtain a silica particle powder, which has a silanol group amount of 0.1 to 1.5 mmol/g as calculated by the following formula from the mass loss when heated from room temperature to 700° C.
• M0 represents the mass of the silica particle powder subjected to thermogravimetric analysis before heating
• M1 represents the mass loss amount when the temperature reached 200°C
• M2 represents the mass loss amount when the temperature reached 700°C
• MH2O represents the molecular weight of a water molecule.
• the polishing composition according to the first aspect wherein a treatment liquid obtained by contacting the silica particles with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is frozen at ⁇ 70° C.
• the polishing composition according to the first aspect wherein a treatment liquid obtained by contacting the silica particle aqueous dispersion with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange, is heated at 140° C. for 2 hours and further heated at 290° C.
• the polishing composition according to any one of the first to fourth aspects, in which the aqueous dispersion of silica particles has been subjected to a thermal history at a temperature of 140° C.
• the polishing composition according to any one of the first to fifth aspects in which the concentration of the silica particles is 1 to 40 mass%.
• the polishing composition according to any one of the first to seventh aspects further comprising at least one additive selected from the group consisting of an acidic compound, a basic compound, a water-soluble compound, a chelating agent, an oxidizing agent, and a metal corrosion inhibitor.
• the basic compound is at least one basic compound selected from the group consisting of alkali metal hydroxides, alkali metal carbonates, alkali metal hydrogencarbonates, and nitrogen-containing basic compounds.
• the polishing composition according to the eighth aspect in which the chelating agent is an aminocarboxylic acid chelating agent or a phosphonic acid chelating agent.
• the polishing composition according to any one of the first to tenth aspects wherein the polishing composition has a pH of 1 to 12.
• a twelfth aspect in a test in which a polishing composition was heated and stored at 50° C. for 28 days, With respect to the average secondary particle diameter measured by dynamic light scattering of the polishing composition before heating and storing at 50° C.
• the polishing composition according to any one of the first to eleventh aspects in which an increase rate of an average secondary particle diameter of the polishing composition measured by a dynamic light scattering method after heating and storing at 50° C. for 28 days is less than 5%.
• the polishing composition according to any one of the first to twelfth aspects which is used for polishing a silicon wafer or a device wafer.
• a method for producing a colloidal silica dispersion as a precursor The method for producing a polishing composition according to any one of the first to thirteenth aspects includes a step of obtaining the silica particle aqueous dispersion by heating the precursor at a temperature of 140° C.
• the silica particle dispersion liquid according to the fifteenth aspect in which the solvent contains water; According to a seventeenth aspect, the silica particle dispersion liquid according to the fifteenth aspect, in which the silica particles have an average secondary particle diameter of 40 to 200 nm as measured by a dynamic light scattering method and an average primary particle diameter of 20 to 100 nm as measured by a nitrogen gas adsorption method; As an eighteenth aspect, the silica particle dispersion according to the fifteenth aspect, wherein a treatment liquid obtained by contacting the silica particle dispersion with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is frozen at ⁇ 70° C.
• the treatment liquid is further freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersion medium, to obtain a silica particle powder, which has a silanol group amount of 0.1 to 1.5 mmol/g as calculated by the following formula from the mass loss when heated from room temperature to 700° C.
• M0 represents the mass of the silica particle powder subjected to thermogravimetric analysis before heating
• M1 represents the mass loss amount when the temperature reached 200°C
• M2 represents the mass loss amount when the temperature reached 700°C
• MH2O represents the molecular weight of a water molecule.
• the silica particle dispersion according to the 15th aspect wherein a treatment liquid obtained by contacting the silica particle dispersion with a cation exchange resin, an anion exchange resin, and a cation exchange resin in this order to perform ion exchange is frozen at ⁇ 70° C.
• the silica particle dispersion according to the fifteenth aspect wherein a treatment liquid obtained by contacting the silica particle dispersion with a cation exchange resin, an anion exchange resin and a cation exchange resin in this order to perform ion exchange, is heated at 140° C. for two hours and further heated at 290° C.
• the silica particle dispersion according to any one of the fifteenth to twentieth aspects, in which the silica particle dispersion has been subjected to a thermal history at a temperature of 140° C.
• a concentration of the silica particles is 1 to 40 mass%.
• a step of preparing a colloidal silica dispersion as a precursor The precursor is heated at a temperature of 140° C. or more and less than 260° C. to obtain the silica particle dispersion.
• the present invention provides a method for producing a silica particle dispersion liquid according to any one of the fifteenth to twenty-second aspects.
• the present invention focuses on the amount of water molecules bound to the surface of silica particles used as abrasive grains, using the Rsp value as an index, which is derived from the relaxation time obtained by pulse NMR measurement of a dispersion of silica particles used as abrasive grains in an aqueous medium and pure water, and has discovered that by setting the Rsp value to a specific value, a high removal rate can be achieved and the storage stability of the polishing composition can be improved. Since high (fast) polishing rate leads to improvement of wafer production efficiency, polishing composition is required to realize high polishing rate.
• silica particles contained in polishing composition if the storage stability of silica particles contained in polishing composition is poor, silica particles will aggregate during storage or transportation to generate minute foreign matter, which may cause a decrease in polishing rate and the generation and increase of defects during polishing, so high storage stability is also required.
• the polishing composition contains silica particles as abrasive grains.
• the interaction between the surface of the silica particles and the aqueous medium in the polishing composition changes depending on the surface condition of the silica particles, and this change in interaction affects the polishing rate and storage stability of the polishing composition.
• the water present on the particle surface or around the particle is classified into bound water and free water according to the state.
• Free water refers to water that exists around the silica particles but does not interact with the silica particles and exists in a free state.
• bound water refers to water that is hydrogen-bonded to the silica particles through the silanol groups on the silica particle surface. This bound water plays an important role in ensuring good contact between the silica particles and water.
• the state (behavior) of water molecules can be known from the relaxation time of protons in water molecules by pulsed NMR measurement.
• the relaxation mechanism in nuclear magnetic resonance (NMR) consists of the process of releasing absorbed energy and the process in which the phase of the precession of aligned nuclear spins becomes fragmented.
• the former is called spin-lattice relaxation (longitudinal relaxation) and its relaxation time is called T1
• spin-spin relaxation transverse relaxation
• T2 relaxation relaxation is most likely to occur when the speed of molecular motion is about the same as the resonance frequency.
• free water molecules that are not in contact with silica particles and water molecules that are in contact with silica particles (bound water) have different response times to magnetic field changes, i.e., relaxation times.
• a short relaxation time is considered to indicate that the particle surface in contact with water is large and the particles are highly dispersible.
• T2 relaxation occurs due to magnetic interactions.
• Measurement of relaxation time by pulsed NMR can be said to be a measurement method that utilizes the difference in T2 relaxation. The presence of this bound water in a specific range effectively improves the polishing rate and storage stability during polishing.
• the present invention by highly controlling the affinity between the silica particles as polishing abrasives and the aqueous medium in the polishing composition, it is possible to achieve both improved polishing speed and improved storage stability, particularly in polishing silicon wafers.
• the silica particle dispersion is a dispersion of silica particles in water or an organic solvent, or a mixed solvent of water and an organic solvent.
• a silica particle aqueous dispersion in which silica particles are dispersed in water, a silica particle organic solvent dispersion in which silica particles are dispersed in an organic solvent, and a silica particle mixed solvent dispersion in which silica particles are dispersed in a mixed solvent of water and an organic solvent are called colloidal silica dispersions or silica sols, and silica particles are sometimes called colloidal silica (colloidal silica).
• the present invention relates to a polishing composition containing an aqueous dispersion of silica particles, the polishing composition having an Rsp value of 0.01 or more and less than 0.15, as described below, derived from the relaxation time obtained by pulse NMR measurement of the aqueous dispersion of silica particles and pure water.
• the present invention also relates to a silica particle dispersion containing a solvent and silica particles, the silica particle dispersion having an Rsp value of 0.01 or more and less than 0.15, as described below, derived from the relaxation time obtained by pulse NMR measurement of the aqueous dispersion of silica particles and pure water.
• the Rsp value is an index showing the affinity of silica particles to a solvent, in particular to water molecules
• Rav is the reciprocal of the relaxation time of a silica particle dispersion (e.g., a silica particle aqueous dispersion) having a silica concentration of 5 mass%
• Rb is the reciprocal of the relaxation time of a solvent (e.g., pure water).
• the Rsp value can be, for example, 0.03 to less than 0.15, 0.05 to less than 0.15, 0.01 to 0.14, 0.03 to 0.14, 0.05 to 0.14, or 0.07 to 0.14.
• the silica particles When the Rsp value is 0.01 or more, the silica particles have a suitable water affinity, and therefore can maintain dispersibility in a solvent or a polishing composition.
• the Rsp value When the Rsp value is less than 0.15, the hydroxyl groups (OH ⁇ ) of the water molecules bound near the surface of the silica particles are few, and excessive dissolution of the silica particle surface by the hydroxyl groups can be suppressed when the silica particles are used as a polishing composition.
• aggregation of the silica particles in an aqueous medium (water) is suppressed, and when a polishing composition containing the silica particles is used for polishing a silicon wafer, the polishing rate is improved and the storage stability of the polishing composition is improved.
• the measurement principle of this technique is based on the fact that solvent molecules in contact with or adsorbed on the particle surface and solvent molecules in the solvent bulk (solvent molecules in a free state that are not in contact with the particle surface) respond differently to changes in magnetic field.
• solvent molecules in contact with or adsorbed on the particle surface and solvent molecules in the solvent bulk respond differently to changes in magnetic field.
• energy transfer occurs when they transition from an excited state to a ground state.
• energy transfer occurs between liquid molecules (solvent molecules) adsorbed on the particle surface via the particle, whereas energy transfer is difficult between liquid molecules (solvent molecules) in the bulk liquid because there is no intermediary between them.
• the NMR relaxation time of the liquid molecules (solvent molecules) adsorbed on the particle surface is shorter than the relaxation time of the molecules in the bulk liquid.
• the relaxation time measured in a silica particle dispersion is the average value of two relaxation times reflecting the liquid volume concentration on the silica particle surface and the liquid volume concentration in the free state (liquid in the bulk liquid but not adsorbed on the particle surface).
• the relaxation time constant R is the reciprocal of the relaxation time T
• Rav (Ps*Rs)+(Pb*Rb) It is calculated by: Rav: average relaxation time constant, that is, the reciprocal of the relaxation time of a silica particle dispersion (for example, an aqueous dispersion of silica particles).
• Ps the volume concentration of the liquid on the particle surface, i.e., the volume concentration of the silica particle dispersion (e.g., the silica particle aqueous dispersion).
• Rs relaxation time constant of the liquid molecules adsorbed on the particle surface, that is, the reciprocal of the relaxation time of the liquid molecules adsorbed on the particle surface.
• Pb volume concentration of bulk liquid, that is, the volume concentration of a blank solution excluding silica particles in a silica particle dispersion (e.g., an aqueous dispersion of silica particles) (in the present invention, for example, pure water is used in the case of an aqueous dispersion, and a solvent having the same composition ratio as the contained solvents is used in the case of an organic solvent dispersion or a mixed solvent dispersion of water and an organic solvent).
• Rb the relaxation time constant of the bulk liquid molecule, i.e., the reciprocal of the relaxation time of a blank solution (e.g., pure water).
• Rav and Rb are the reciprocals of the relaxation times (transverse relaxation time T2, specifically, the NMR relaxation time after the silica abrasive grains are dispersed, and the NMR relaxation time of a blank solution (e.g., pure water)) measured using a pulse NMR device (product name) Acorn area manufactured by Xigo nanotools.
• the measurement conditions can be set as follows: magnetic field: 0.3 T, measurement frequency: 13 MHz, measurement nucleus: 1 H NMR, measurement method: CPMG pulse sequence method, sample amount: 0.77 mL, and temperature: 30°C.
• Rsp is an index of the affinity of the particle surface with the solvent. When the specific surface area of silica particles is the same, the larger this value (Rsp) is, the higher the affinity with the solvent is, and particularly when the solvent is aqueous, the higher the hydrophilicity is.
• the average primary particle size of the colloidal silica dispersion refers to the average primary particle size of the silica particles that are the dispersoid.
• the average primary particle size of the colloidal silica dispersion refers to a particle size calculated from a specific surface area obtained by measurement using a nitrogen gas adsorption method (BET method), unless otherwise specified.
• the average primary particle diameter of the silica particles is, for example, 20 to 100 nm, and can be, for example, 20 to 85 nm, 30 to 70 nm, or 35 to 60 nm.
• the frequency of contact between the silica particles in the polishing composition can be reduced, thereby improving storage stability.
• an average primary particle diameter of the silica particles of 100 nm or less, the occurrence of defects due to scratches caused by rubbing the silica particles against the surface of a silicon wafer when used for polishing a silicon wafer can be reduced.
• the silica particles settle in the polishing composition, and the silica particles are prevented from adhering to each other at the bottom of a storage container, thereby improving the storage stability of the polishing composition.
• the average secondary particle diameter and the dispersion state (whether the silica particles are in a dispersed state or an aggregated state) of the silica particles in the silica particle dispersion or the polishing composition can be determined by measurement using a dynamic light scattering method.
• the average secondary particle size indicates the average value of secondary particle size (dispersed particle size), and the average secondary particle size in a completely dispersed state is said to be about 1.2 to 2 times the average primary particle size (specific surface area diameter obtained by measurement using the nitrogen gas adsorption method (BET method) or the Sears method, and indicates the average value of primary particle size).
• the average secondary particle diameter of the silica particles i.e., for example, colloidal silica dispersion (colloidal silica particles), measured by dynamic light scattering may be, for example, 40 to 200 nm, or 40 to 150 nm, 40 to 100 nm, or 50 to 80 nm.
• the average secondary particle diameter of the silica particles measured by dynamic light scattering is measured using a Zetasizer Nano (product name, manufactured by Malvern Panalytical Co., Ltd.) device in accordance with ISO 22412:2017.
• the average secondary particle diameter refers to the Z-average particle diameter measured by dynamic light scattering.
• the polishing composition containing the silica particle aqueous dispersion of the present invention can have a polyvalent metal impurity content of 1 to 100 ppm/SiO 2 , 1 to 50 ppm/SiO 2 , or 1 to 40 ppm/SiO 2 .
• the silica particle dispersion of the present invention may have a polyvalent metal impurity content of 1 to 100 ppm/SiO 2 , 1 to 50 ppm/SiO 2 , or 1 to 40 ppm/SiO 2 .
• the amount of polyvalent metal impurities contained in the polishing composition within the above range, it is possible to suppress changes in the pH or electrolyte concentration of the polishing composition due to leaching of polyvalent metal impurities from within the silica particles, or deterioration of the dispersion stability of the silica particles due to the cationized polyvalent metal in the polishing composition acting as an agglomerating agent for the silica particles.
• the amount of polyvalent metal impurities contained in the silica particle dispersion is within the above range, it is possible to suppress changes in the pH or electrolyte concentration of the silica particle dispersion due to elution of the polyvalent metal impurities from within the silica particles, or deterioration in the dispersion stability of the silica particles due to the cationized polyvalent metal in the silica particle dispersion acting as an aggregating agent for the silica particles, which can be suppressed.
• the amount of polyvalent metal impurities contained in the silica particle dispersion liquid within the above range, the amount of polyvalent metal impurities contained in the silica particles can be controlled, the network of Si-O-Si bonds constituting the skeleton of the silica particles becomes dense, and excessive dissolution of the silica particle surface by hydroxyl groups can be suppressed.
• the polishing rate when used for polishing silicon wafers can be further improved, and the storage stability of the polishing composition can be improved.
• polyvalent metal impurities examples include iron, aluminum, calcium, magnesium, titanium, zirconium, copper, nickel, chromium, zinc, lead, etc.
• the amount of polyvalent metal impurities can be analyzed by pretreating the polishing composition or the silica particle dispersion and completely dissolving the silica particles contained in the composition or the dispersion, and then by inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AA), or the like.
• ICP-OES inductively coupled plasma optical emission spectrometry
• ICP-MS inductively coupled plasma mass spectrometry
• AA atomic absorption spectrometry
• nitric acid 0.3 mL of 61% by mass nitric acid is added to the obtained dried product, and then pure water is added so that the total mass of the dried product, nitric acid, and pure water is 3 g, to obtain a sample for metal impurity analysis.
• the silica particles contained in the polishing composition or silica particle dispersion of the present invention can have a predetermined amount of silanol groups. That is, the silica particle powder obtained by freeze-drying the colloidal silica dispersion containing the silica particles at room temperature under a pressure of 5 Pa or less to remove the dispersion medium can have a silanol group amount calculated by the following formula from the mass loss when heated from room temperature to 700° C.
• thermogravimetric analysis and the molecular weight of water molecules of, for example, 0.1 to 1.5 mmol/g, 0.3 to 1.5 mmol/g, 0.5 to 1.5 mmol/g, 0.3 to 1.4 mmol/g, 0.5 to 1.4 mmol/g, 0.3 to 1.3 mmol/g, or 0.3 to 1.3 mmol/g.
• M0 represents the mass of the silica particle powder subjected to thermogravimetric analysis before heating
• M1 represents the amount of mass loss when the temperature reached 200°C
• M2 represents the amount of mass loss when the temperature reached 700°C
• MH2O represents the molecular weight of a water molecule.
• the target silica particle dispersion liquid is first contacted with a cation exchange resin, an anion exchange resin, and a cation exchange resin in that order to obtain an ion-exchanged liquid.
• the ion-exchanged liquid is frozen at -70°C to -80°C, and then freeze-dried at room temperature under a pressure of 5 Pa or less to remove the dispersing medium, thereby obtaining the desired silica particle powder.
• Silica particles have silanol groups on their surfaces, and the silanol groups are prone to adsorb water through hydrogen bonds. Therefore, in order to quantify the amount of silanol groups in silica particles from the amount of mass loss due to heating, it is preferable to remove the adsorbed water by heating to about 200° C., at which point the adsorbed water is desorbed, as described above.
• the amount of silanol groups in the silica particles is more than the above, for example, 1.5 mmol/g, when two silica particles come into contact with each other, they are likely to bond with each other, and the stability of the polishing composition or the silica particle dispersion liquid is deteriorated. If the amount of silanol groups in the silica particles is less than the above, for example, 0.1 mmol/g, the silica particle surface is not sufficiently solvated in the polar solvent, so that the silica particle surface cannot maintain dispersibility and aggregates and precipitates, and the stability of the polishing composition or the silica particle dispersion liquid is deteriorated.
• the silica particles contained in the polishing composition or silica particle dispersion of the present invention can have a predetermined density. That is, the silica particle powder obtained by freeze-drying the colloidal silica dispersion containing the silica particles at room temperature under a pressure of 5 Pa or less to remove the dispersion medium can have a density measured by dry density measurement of, for example, 2.20 to 2.35 g/cm 3 , 2.22 to 2.35 g/cm 3 , 2.25 to 2.35 g/cm 3 , 2.27 to 2.35 g/cm 3 , 2.25 to 2.33 g/cm 3 , 2.25 to 2.30 g/cm 3 , or 2.27 to 2.30 g/cm 3 .
• the procedure for obtaining silica particle powder by freeze-drying is the same as that described for the quantitative determination of the amount of silanol groups.
• the density of the silica particles contained in the polishing composition or silica particle dispersion liquid being 2.20 g/cm 3 or more, or 2.25 g/cm 3 or more, the network of Si-O-Si bonds constituting the skeleton of the silica particles becomes dense, and the adsorption and desorption of impurities such as metal ions is suppressed, so that the dispersibility of the silica particles can be prevented from deteriorating due to the variation in pH, electrolyte concentration or composition balance of the polishing composition or silica particle dispersion liquid.
• the density of the silica particles contained in the polishing composition or silica particle dispersion liquid being 2.35 g/cm 3 or less, it is possible to suppress the silica particles from settling in the polishing composition or silica particle dispersion liquid and bonding to each other, or adhesion to the container. As a result, it is possible to further improve the polishing rate when used for polishing silicon wafers, and to improve the storage stability of the polishing composition.
• the silica particles contained in the polishing composition or silica particle dispersion of the present invention can have a predetermined ratio between the specific surface area based on the water vapor adsorption method and the specific surface area based on the nitrogen gas adsorption method.
• the ratio (S H2O /S N2 ) of the specific surface area (S H2O ) based on the nitrogen gas adsorption method (BET method) obtained by BET analysis from the relationship between the amount of water vapor adsorption and the relative humidity to the specific surface area (S N2 ) based on the nitrogen gas adsorption method (BET method) described in ⁇ Particle diameter ⁇ average primary particle diameter, average secondary particle diameter>> can be, for example, 0.10 to 0.65, 0.15 to 0.65 , 0.20 to 0.65, 0.10 to 0.60, 0.10 to 0.50, 0.10 to 0.40, 0.20 to 0.60, 0.25 to 0.60, 0.25 to 0.50, or 0.25 to 0.40.
• the specific surface area (S H2O ) based on the water vapor adsorption method can be determined by performing BET analysis on the water vapor adsorption amount of silica particles measured using a water vapor adsorption/desorption measuring device and the relative humidity in the range of relative humidity 0.20 to 0.35.
• the target silica particle dispersion liquid is first contacted with a cation exchange resin, an anion exchange resin, and a cation exchange resin in that order to obtain an ion exchange treatment liquid.
• the ion exchange liquid is heated at 140°C for 2 hours to remove most of the dispersion medium, and then heated at 290°C for 1 hour to completely remove the dispersion medium.
• the desired silica particle powder can be obtained by grinding in a mortar for 10 minutes.
• silanol groups are present on the surface of silica particles, and the silanol groups are prone to adsorb water through hydrogen bonds. Therefore, in order to quantify the specific surface area based on the water vapor adsorption method, it is preferable to remove the adsorbed water by heating at 200° C. for 1 hour immediately before the measurement, at which the adsorbed water is desorbed as described above.
• the ratio of the specific surface area based on the water vapor adsorption method and the specific surface area based on the nitrogen gas adsorption method is larger than the above, for example, 0.65, the hydrophilicity of the silica particle surface is high, and many hydroxyl groups ( OH- ) in the composition are adsorbed on the particle surface, and the silanol bond on the silica particle surface may be cleaved and dissolution may proceed.
• the dissolution of silica particles proceeds, the highly active silanol groups inside the silica particles are exposed on the silica particle surface, and the silica particles proceed to aggregate with each other, which may deteriorate the storage stability of the polishing composition or silica particle dispersion.
• the ratio is smaller than the above, for example, 0.10, the hydrophilicity of the silica particle surface is low, and it is not sufficiently solvated in a polar solvent, so that it cannot maintain dispersibility and aggregates and precipitates, which may
• the method for producing the colloidal silica dispersion (silica sol) used in the present invention can be roughly divided into a step (I) of obtaining active silicic acid, a step (II) of preparing a precursor silica sol, a step (III) of further heating the precursor silica sol, and a step (IV) of concentrating the obtained silica sol.
• Step (I) The step (I) of obtaining active silicic acid is divided into a step (a1) of obtaining active silicic acid and a step (a2) of purifying it.
• the step (a1) is essential, and the step (a2) is not essential but is performed as desired.
• steps (a1) and (a2) can be carried out as follows.
• Step (a1) An aqueous solution of an alkali metal silicate containing 300 to 10,000 ppm of metal oxides other than silica relative to silica is diluted with pure water to a concentration of 1 to 6 mass% as SiO2 derived from the silicate, and then contacted with a hydrogen-type strongly acidic cation exchange resin to obtain an aqueous solution of active silicic acid having a SiO2 concentration of 1 to 6 mass%.
• Step (a2) To the aqueous activated silicic acid solution obtained in step (a1), an acid selected from mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid is added to adjust the pH to 1 to 2, and the solution is left for 12 hours or more.
• an acid selected from mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid is added to adjust the pH to 1 to 2, and the solution is left for 12 hours or more.
• metal oxides other than silica are dissolved and ionized, and the solution is contacted with a hydrogen-type strongly acidic cation exchange resin to remove the dissolved metal ions, and then contacted with a hydroxide-type strongly basic anion exchange resin to remove the anions, to obtain purified activated silicic acid with a SiO2 concentration of 1 to 6 mass %.
• the alkali metal silicate sodium water glass, which is an inexpensive industrial product and has a SiO 2 /Na 2 O molar ratio of about 2 to 4.
• the main polyvalent metals contained in relatively large amounts are aluminum, iron, calcium, magnesium, etc.
• the alkali metal silicate aqueous solution can be brought into contact with the hydrogen-type strongly acidic cation exchange resin by passing the alkali metal silicate aqueous solution through a column packed with the ion exchange resin. The liquid passing through the column is recovered as an aqueous solution of active silicic acid having a SiO2 concentration of 1 to 6 mass %, preferably 2 to 6 mass %.
• the amount of hydrogen ion exchange resin used may be an amount sufficient to exchange the total amount of alkali metal ions in the aqueous alkali metal silicate solution with hydrogen ions, and specifically, the amount is preferably such that the exchange capacity of the hydrogen ion exchange resin is 1 to 5 times, 1 to 3 times, or 1 to 2 times the total amount of alkali metal ions contained in the aqueous alkali metal silicate solution on an equivalent basis.
• the speed of passage through the column is preferably a space velocity of about 1 to 10 per hour.
• Step (II) of preparing a precursor silica sol is, for example, a step of carrying out the following steps (b) and (c), or a step of preparing a commercially available silica sol.
• the aqueous solution of sodium hydroxide or potassium hydroxide used in step (b) is preferably obtained by dissolving commercially available industrial sodium hydroxide or potassium hydroxide with a purity of 95% by mass or more in industrial water or ion-exchanged water from which cations have been removed, preferably to a concentration of 2 to 20% by mass.
• the equipment used in step (c) may be a normal acid-resistant, alkali-resistant and pressure-resistant vessel equipped with a stirrer, a temperature control device, a liquid level sensor, a pressure reducing device, a liquid supply device, the above-mentioned cooling device, etc.
• the liquid temperature in the vessel is kept at 110 to less than 160°C.
• Step (III) of further heating the precursor silica sol includes the following steps (d), (e) and (f). Among the steps, step (f) is essential, and steps (d) and (e) are not essential but are carried out as desired.
• Step (d) or step (e) can be carried out before step (f). Either step (d) or step (e) may be carried out, or both may be carried out, or neither may be carried out. When both are carried out, either step (d) or step (e) may be carried out first.
• the liquid temperature in the container is kept at 160 to less than 300°C.
• the step (IV) of further concentrating the obtained silica sol is a step of concentrating the silica sol obtained in the step (III) to 10 to 50 mass %.
• This step (IV) is not essential but is performed as desired.
• a known concentrating device such as a concentrator equipped with an ultrafiltration membrane or a reduced pressure concentrator can be used.
• the polishing composition of the present invention can contain, in addition to silica particles as abrasive grains and water as an aqueous medium, at least one additive selected from the group consisting of acidic compounds, basic compounds, water-soluble compounds, chelating agents, oxidizing agents, and metal corrosion inhibitors.
• the silica particle dispersion of the present invention can contain, in addition to silica particles and water or an organic solvent, or a mixed solvent of water and an organic solvent, at least one additive selected from the group consisting of acidic compounds and basic compounds.
• the mass percentage of the solid content excluding water as the aqueous medium from the polishing composition can be, for example, 0.01 to 40 mass%, 0.01 to 30 mass%, 0.01 to 20 mass%, 0.1 to 40 mass%, 0.1 to 20 mass%, or 0.1 to 15 mass%, and the mass percentage of the silica particles in the solid content can be 80 to 100 mass%, or 85 to 99.9 mass%.
• the mass percentage of the silica particles in the polishing composition or silica particle dispersion can be 1 to 40 mass%, 1 to 30 mass%, 1 to 20 mass%, or 3 to 30 mass%.
• the solid content excluding the aqueous medium from the polishing composition 0.01 mass% or more, excessive dissolution of the silica particle surface by hydroxyl groups can be suppressed.
• the solid content excluding the aqueous medium from the polishing composition 40 mass% or less the increase in the number of silica particles in the polishing composition and the increase in the frequency of contact between silica particles due to the decrease in the amount of solvent can be prevented, and aggregation can be suppressed.
• the viscosity of the polishing composition can be suppressed from becoming excessively high, making it easier to handle. As a result, the storage stability of the polishing composition is improved, making it easier to store or transport.
• the amount of solids in the polishing composition or silica particle dispersion can be measured, for example, by heating the composition in an electric furnace at 1000° C. for 1 hour and weighing the residue.
• the acidic compound may be a mineral acid such as hydrochloric acid, sulfuric acid, nitric acid, or phosphoric acid, or an organic acid such as formic acid, oxalic acid, citric acid, acetic acid, lactic acid, malic acid, malonic acid, succinic acid, tartaric acid, butyric acid, fumaric acid, benzoic acid, glycolic acid, propionic acid, or ascorbic acid.
• the acidic compound may be used alone or in combination of two or more of them.
• Examples of the basic compound include hydroxides of alkali metals, carbonates of alkali metals, hydrogencarbonates of alkali metals, nitrogen-containing basic compounds, etc.
• the basic compound may be used alone or in combination of two or more kinds selected from these.
• sodium hydrogen carbonate or potassium hydrogen carbonate as the hydrogen carbonate of an alkali metal.
• sodium carbonate or potassium carbonate as the carbonate of an alkali metal.
• ammonia or a quaternary ammonium salt as the nitrogen-containing basic compound, and it is more preferable to use a quaternary ammonium compound from the viewpoint of achieving a high polishing rate.
• a quaternary ammonium compound it is possible to use tetramethylammonium hydroxide, ethyltrimethylammonium hydroxide, diethyldimethylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, or a salt thereof.
• the basic compound can be blended in the polishing composition at a ratio of, for example, 0.1 to 50 mass%, 0.1 to 30 mass%, 0.1 to 10 mass%, 1 to 50 mass%, 1 to 30 mass%, or 1 to 10 mass% relative to the silica particles.
• the pH of the polishing composition can be prevented from excessively increasing or decreasing, and the stability of the polishing composition can be improved.
• the pH of the polishing composition according to the present invention can be adjusted to the range of 1 to 12, 1 to 6, 3 to 6, 7 to 12, 7 to 10, 8 to 11, or 10 to 12.
• the pH of the polishing composition can be adjusted to the above range, when the polishing composition is used to polish a silicon wafer, the Si bonds on the silicon wafer surface are broken by the acid or base, and the silicon wafer surface is easily scraped by the silica particles, thereby improving the polishing rate.
• the pH of the silica particle dispersion liquid according to the present invention can be adjusted to the range of 8 to 11, 8 to 10, or 9 to 10. By adjusting the pH to the above range, the dispersibility of the silica particles can be improved, and aggregation of the silica particles in the solvent can be suppressed.
• Any water-soluble compound can be used as the water-soluble compound.
• monomers having a carboxylic acid group such as acrylic acid, methacrylic acid, maleic acid, and the like, and their polymers such as polyacrylic acid and polymethacrylic acid, and their salts such as ammonium polyacrylate, potassium polyacrylate, ammonium polymethacrylate, and potassium polymethacrylate can be used.
• alginic acid, pectinic acid, carboxymethyl cellulose, polyaspartic acid, polyglutamic acid, polyamic acid, ammonium polyamic acid, polyvinylpyrrolidone, hydroxyethyl cellulose, hydroxypropyl cellulose, glycerin, polyglycerin, polyvinyl alcohol, polyacrylamide and its derivatives, polymethacrylamide and its derivatives, or carboxyl group- or sulfonic acid group-modified polyvinyl alcohol can be used.
• the water-soluble compound can be blended in the polishing composition at a ratio of, for example, 0.01 to 10 mass%, 0.01 to 5 mass%, 0.01 to 3 mass%, 0.05 to 10 mass%, 0.1 to 10 mass%, or 0.05 to 5 mass% relative to the silica particles.
• the blending amount of the water-soluble compound within the above range, the dispersion stability of the silica particles contained in the polishing composition can be improved, while protecting the silicon wafer surface other than the convex parts on which the load is concentrated when the silicon wafer is polished, thereby improving the flatness of the silicon wafer.
• an aminocarboxylic acid-based chelating agent or a phosphonic acid-based chelating agent can be used as the chelating agent.
• the aminocarboxylic acid chelating agent include ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, triethylenetetraminehexaacetic acid, 1,3-propanediaminetetraacetic acid, 1,3-diamine-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, glycol ether diaminetetraacetic acid, dicarboxymethyl glutamic acid, and ethylenediamine-N,N'-disuccinic acid.
• the phosphonic acid chelating agent examples include hydroxyethylidene diphosphonic acid, nitrilotris(methylene phosphonic acid), phosphonobutane tricarboxylic acid, and ethylenediaminetetra(methylene phosphonic acid).
• the chelating agent can be blended in the polishing composition at a ratio of, for example, 0.01 to 10 mass%, 0.01 to 5 mass%, 0.01 to 3 mass%, 0.05 to 10 mass%, 0.1 to 10 mass%, or 0.05 to 5 mass% relative to the silica particles. By blending the amount of the chelating agent in the above range, it is possible to improve the dispersion stability of the silica particles contained in the polishing composition while reducing contamination of the silicon wafer by metal impurities.
• the oxidizing agent examples include hydrogen peroxide, potassium permanganate, potassium periodate, hypochlorous acid, and ozone water.
• the oxidizing agent can be blended in the polishing composition at a ratio of, for example, 0.01 to 10 mass%, 0.01 to 5 mass%, 0.01 to 3 mass%, 0.05 to 10 mass%, 0.1 to 10 mass%, or 0.05 to 5 mass% relative to the silica particles.
• metal corrosion inhibitor examples include triazole compounds, pyridine compounds, pyrazole compounds, pyrimidine compounds, imidazole compounds, guanidine compounds, thiazole compounds, tetrazole compounds, triazine compounds, and hexamethylenetetramine.
• the triazole compounds include 1,2,3-triazole, 1,2,4-triazole, 3-amino-1H-1,2,4-triazole, benzotriazole (BTA), 1-hydroxybenzotriazole, 1-hydroxypropylbenzotriazole, 2,3-dicarboxypropylbenzotriazole, 4-hydroxybenzotriazole, 4-carboxy-1H-benzotriazole, 4-carboxy-1H-benzotriazole methyl ester (1H-benzotriazole-4-carboxylate methyl), 4-carboxy-1H-benzotriazole butyl ester (1H-benzotriazole-4-carboxylate butyl), 4-carboxy-1H-benzotriazole octyl ester (1H-benzotriazole-4-carboxylate octyl), 5-hexylbenzotriazole, (1,2,3-benzotriazolyl-1-methyl) (1,2,4-triazole), Azolyl-1-methyl)
• the pyridine compounds include pyridine, 8-hydroxyquinoline, prothionamide, 2-nitropyridin-3-ol, pyridoxamine, nicotinamide, iproniazid, isonicotinic acid, benzo[f]quinoline, 2,5-pyridinedicarboxylic acid, 4-styrylpyridine, anabasine, 4-nitropyridine-1-oxide, pyridine-3-ethyl acetate, quinoline, 2-ethylpyridine, quinolinic acid, arecoline, citrazinic acid, pyridine-3-methanol, 2-methyl-5-ethylpyridine, 2-fluoropyridine, pentafluoropyridine, 6-methylpyridin-3-ol, and pyridine-2-ethyl acetate.
• the pyrazole compounds include pyrazole, 1-allyl-3,5-dimethylpyrazole, 3,5-di(2-pyridyl)pyrazole, 3,5-diisopropylpyrazole, 3,5-dimethyl-1-hydroxymethylpyrazole, 3,5-dimethyl-1-phenylpyrazole, 3,5-dimethylpyrazole, 3-amino-5-hydroxypyrazole, 4-methylpyrazole, N-methylpyrazole, 3-aminopyrazole, and 3-aminopyrazole.
• the pyrimidine compounds include pyrimidine, 1,3-diphenyl-pyrimidine-2,4,6-trione, 1,4,5,6-tetrahydropyrimidine, 2,4,5,6-tetraaminopyrimidine sulfate, 2,4,5-trihydroxypyrimidine, 2,4,6-triaminopyrimidine, 2,4,6-trichloropyrimidine, 2,4,6-trimethoxypyrimidine, 2,4,6-triphenylpyrimidine, 2,4-diamino-6-hydroxylpyrimidine, 2,4-diaminopyrimidine, 2-acetamidopyrimidine, 2-aminopyrimidine, 4-aminopyrazolo[3,4-d]pyrimidine, and the like.
• the imidazole compounds include imidazole, 1,1'-carbonylbis-1H-imidazole, 1,1'-oxalyldiimidazole, 1,2,4,5-tetramethylimidazole, 1,2-dimethyl-5-nitroimidazole, 1,2-dimethylimidazole, 1-(3-aminopropyl)imidazole, 1-butylimidazole, 1-ethylimidazole, 1-methylimidazole, benzimidazole, and the like.
• the guanidine compounds include guanidine, 1,1,3,3-tetramethylguanidine, 1,2,3-triphenylguanidine, 1,3-di-o-tolylguanidine, 1,3-diphenylguanidine, etc.
• the thiazole compounds include thiazole, 2-mercaptobenzothiazole, 2,4-dimethylthiazole, etc.
• tetrazole compounds examples include tetrazole, 5-methyltetrazole, 5-amino-1H-tetrazole, 1-(2-dimethylaminoethyl)-5-mercaptotetrazole, etc.
• the triazine compounds include triazine, 3,4-dihydro-3-hydroxy-4-oxo-1,2,4-triazine, etc.
• the metal corrosion inhibitor can be blended into the polishing composition in a ratio of, for example, 0.0001 to 10% by mass relative to the silica particles. By blending the amount of metal corrosion inhibitor within the above range, it is possible to improve the stability of the polishing composition while maintaining the anticorrosive effect.
• polishing composition of the present invention is heated and stored at 50°C for 28 days, it is desirable that the rate of increase in the average secondary particle diameter of the polishing composition after heated storage at 50°C for 28 days, as measured by dynamic light scattering, is low (particle diameter does not change) compared to the average secondary particle diameter of the polishing composition before heated storage, and the increase can be, for example, less than 5%, and can be 4% or less, 0 to less than 5%, 0 to 4%, or 0 to 3%.
• a polishing composition that satisfies the above-mentioned increase rate hardly changes the particle size or shape of the silica particles contained in the polishing composition even during transportation or storage, so that the generation of coarse particles due to aggregation of silica particles and the reduction in the amount of active ingredient due to settling of silica particles do not occur, and the desired polishing performance can be achieved.
• the polishing composition of the present invention can be manufactured, stored and transported in the form of a concentrated liquid.
• the silica concentration in the form of the concentrated liquid is not particularly limited as long as it satisfies the increase rate of the average secondary particle diameter in the test of heating and storing at 50°C for 28 days, and can be, for example, 1 to 30 mass%, 5 to 30 mass%, 5 to 25 mass%, or 10 to 25 mass%.
• the concentrated liquid can be diluted with any solvent such as pure water immediately before use, and adjusted to a predetermined SiO 2 concentration, for example, 0.1 to 10 mass%, and then used for polishing.
• the pH of the concentrate can be adjusted to within the range of 1-12, 1-6, 3-6, 7-12, 7-10, 8-12, 9-12, 10-12, or 11-12.
• the polishing composition of the present invention can be used for polishing silicon wafers or device wafers. There are single-sided polishing and double-sided polishing machines, and in either machine, the polishing composition of the present invention can be used to polish silicon wafers.
• the polishing process of silicon wafers is usually composed of multiple stages of polishing, including a primary polishing performed at the beginning of the polishing process and a finish polishing performed after the primary polishing process.
• the primary polishing and the finish polishing may each be performed in two stages.
• the polishing composition of the present invention may be used in both the primary polishing and the finish polishing, or the polishing composition of the present invention may be used in only one of the primary polishing and the finish polishing.
• the polishing composition of the present invention may be used by circulating in the polishing machine in each polishing process, or may be used as a flow-through that is used only once.
• the polishing composition of the present invention can also be used for CMP polishing of device wafers.
• the silica particle dispersion of the present invention can be suitably used in a polishing composition.
• Synthesis of colloidal silica dispersion Synthesis of colloidal silica dispersion A
• a sodium silicate aqueous solution of JIS No. 3 was prepared.
• the SiO2 concentration was 28.8 mass% and the Na2O concentration was 9.47 mass%.
• the above sodium silicate aqueous solution was diluted with pure water to prepare a sodium silicate aqueous solution (a) having a SiO2 concentration of 4 mass%.
• a sodium silicate aqueous solution (a) was passed through a column packed with a hydrogen-type strongly acidic cation exchange resin (trade name) Amberlite IR-120B at a space velocity of 4.5 per hour to remove cations, thereby preparing an active silicic acid aqueous solution.
• the obtained active silicic acid aqueous solution was adjusted to pH 8.5 to 9.5 by adding 10% by mass of sodium hydroxide aqueous solution to obtain a stabilized active silicic acid aqueous solution.
• the SiO2 concentration of the obtained stabilized active silicic acid aqueous solution was 3.2% by mass.
• 2400 g of the stabilized activated silicic acid aqueous solution obtained above was placed in a reaction apparatus comprising a 3 L SUS pressure vessel equipped with a stirrer, a heater, etc., and the liquid temperature in the vessel was adjusted by heating to 130 to 150° C.
• the vessel was heated for 2 hours and 30 minutes while maintaining the temperature in the vessel at 130 to 150° C., thereby obtaining a colloidal silica dispersion (precursor silica sol) having an average primary particle size of 10 to 15 nm.
• the obtained colloidal silica dispersion was concentrated to a SiO2 concentration of 33 mass% at room temperature using a commercially available ultrafiltration device equipped with a polysulfone ultrafiltration membrane with a molecular weight cutoff of 200,000 (Advantec Co., Ltd. (product name) Q2000 150E), thereby obtaining a precursor silica sol with an adjusted SiO2 concentration.
• the precursor silica sol with the adjusted SiO2 concentration was passed through a column packed with a hydrogen-type strongly acidic cation exchange resin (product name) Amberlite IR-120B at a space velocity of 10 per hour to remove cations, and a 10% by mass aqueous solution of sodium hydroxide was added to the resulting dispersion to adjust the pH to 7 to 8, thereby obtaining a precursor silica sol with an adjusted pH.
• the precursor silica sol with the SiO2 concentration and pH adjusted obtained above was placed in a reaction apparatus equipped with a stirrer, a heating device, etc., in a 3 L SUS pressure-resistant container, and the liquid temperature in the container was adjusted to 220 to 240° C. by heating. After the temperature in the container reached 220 to 240° C., the container was heated for 2 hours and 20 minutes while maintaining the temperature in the container at 220 to 240° C., thereby obtaining a colloidal silica dispersion A.
• Synthesis Example 2 Synthesis of colloidal silica dispersion B Colloidal silica dispersion B was obtained in the same manner as in Synthesis Example 1, except that the precursor silica sol having the adjusted SiO2 concentration and pH was heated at 210 to 230°C using a SUS pressure vessel.
• Synthesis Example 4 Synthesis of colloidal silica dispersion D Colloidal silica dispersion B adjusted to pH 9 to 10 was heated at 170 to 190° C. for 72 hours in a SUS pressure vessel, and the same procedure as in Synthesis Example 3 was repeated to obtain colloidal silica dispersion D.
• Synthesis Example 5 Synthesis of colloidal silica dispersion E A colloidal silica dispersion E was obtained in the same manner as in Synthesis Example 1, except that the precursor silica sol having the adjusted SiO2 concentration and pH was heated at 230 to 250°C for 6 hours using a SUS pressure vessel.
• Synthesis Example 6 Synthesis of colloidal silica dispersion F Colloidal silica dispersion F was obtained in the same manner as in Synthesis Example 1, except that the precursor silica sol having the adjusted SiO2 concentration and pH was heated at 240 to 260°C for 9 hours using a SUS pressure vessel.
• Synthesis Example 7 Synthesis of colloidal silica dispersion G Colloidal silica dispersion G was synthesized in the same manner as in Synthesis Example 4 of WO 2020/091000. Specifically, an active silicic acid aqueous solution stabilized with sulfuric acid was obtained by adding 8% by mass of sulfuric acid to the active silicic acid aqueous solution obtained by the same operation as in Synthesis Example 1 to adjust the pH to 2-3. Pure water was added to the active silicic acid aqueous solution stabilized with sulfuric acid obtained above under stirring, and then a 10% by mass aqueous potassium hydroxide solution was added to adjust the SiO 2 concentration to 3.2% by mass and the pH to 12.0.
• the liquid temperature in the container was adjusted to 110-130°C using a reaction device equipped with a stirrer, a heater, etc. in a SUS pressure-resistant container with an internal volume of 3L.
• the aqueous solution of active silicic acid stabilized with sulfuric acid obtained above was continuously fed as a feed liquid while maintaining the inside of the container at 110-130°C until the pH of the reaction liquid reached 11.4.
• the temperature inside the vessel was kept at 110° C. and the reaction was allowed to proceed for 1 hour.
• the aqueous solution of active silicic acid stabilized with sulfuric acid was continuously supplied as a supply liquid until the pH of the reaction liquid reached 11.1.
• the temperature inside the vessel was kept at 110 to 130° C. and the reaction liquid was obtained by heating for another 2 hours.
• the obtained reaction solution was concentrated at room temperature to a SiO2 concentration of 40 mass% using a commercially available ultrafiltration device equipped with a polysulfone ultrafiltration membrane with a molecular weight cutoff of 200,000 (product name: Q2000 150E, manufactured by Advantec Co., Ltd.), to obtain a colloidal silica dispersion G.
• the average primary particle size of the silica particles was measured by a nitrogen gas adsorption method. Pure water was added to each colloidal silica dispersion to prepare a sample with an SiO2 concentration adjusted to 10% by mass. Next, 10 mL of hydrogen-type strong acid cation exchange resin Amberlite (trade name) IR-120B was added to 5 g of the obtained sample and stirred for 30 minutes to obtain a sample from which cations had been removed. The obtained sample was filtered through a nylon mesh to remove the cation exchange resin, and then heated at 290° C.
• the average secondary particle size of silica particles was measured by dynamic light scattering (DLS) using a Zetasizer Nano (trade name, manufactured by Malvern Panalytical) as follows. 0.1 g of colloidal silica dispersion was taken into a polystyrene cell with an optical path length of 10 mm, and a 0.15 mass % aqueous sodium chloride solution was added to obtain a colloidal silica dispersion in which the silica concentration was adjusted so that the count rate when the attenuator was set to 7 was 200 to 400 kcps.
• DLS dynamic light scattering
• the amount of the prepared colloidal silica dispersion put into the cell was adjusted so that the height of the liquid surface from the bottom of the cell was about 1 cm, and the average secondary particle size of silica was measured under conditions of an attenuator of 7 and a temperature of 22.0°C.
• the obtained sample was filtered through a nylon mesh to remove the anion exchange resin, and then 20 mL of hydrogen-type strong acid cation exchange resin Amberlite (trade name) IR-120B was added again and stirred for 30 minutes to remove the cations.
• the obtained sample was filtered through a nylon mesh to remove the cation exchange resin, and a dispersion from which cations and anions were removed was obtained.
• the dispersion from which the ions were removed was placed in a 300 mL eggplant flask.
• the eggplant flask containing the dispersion was immersed for 10 minutes in ethanol cooled to -70°C to -80°C by adding dry ice, to obtain a frozen dispersion.
• the frozen dispersion was left to stand at room temperature under a vacuum of 5 Pa or less using a freeze-drying device (product name FDU-2100, manufactured by Tokyo Rikakikai Co., Ltd.), to sublimate the frozen moisture and obtain a freeze-dried sample.
• the freeze-dried sample was ground in an agate mortar for 10 minutes to obtain a freeze-dried powder.
• the freeze-dried powder was heated from room temperature to 700° C. using a thermogravimetric differential thermal analyzer (product name TG-DTA2000SA, manufactured by Bruker Corporation), and the amount of mass loss was measured when the temperature was increased from room temperature to 700° C.
• TG-DTA2000SA thermogravimetric differential thermal analyzer
• 5 to 10 mg of the freeze-dried powder was placed in a platinum container, and the initial sample mass was M0.
• the platinum container containing the freeze-dried powder was placed in a thermogravimetric differential thermal analyzer, and heated in a nitrogen gas atmosphere from room temperature to 700°C at a heating rate of 10°C/min. The flow rate of the nitrogen gas was 100cc/min.
• Amount of silanol groups (mmol/g) 2 ⁇ (M2 ⁇ M1) ⁇ 18 ⁇ (M0 ⁇ M1) ⁇ 1000
• the obtained sample was filtered through a nylon mesh to remove the anion exchange resin, and then 20 mL of hydrogen-type strong acid cation exchange resin Amberlite (trade name) IR-120B was added again and stirred for 30 minutes to remove the cations.
• the obtained sample was filtered through a nylon mesh to remove the cation exchange resin, and a dispersion from which cations and anions were removed was obtained. 20 g of the dispersion was weighed out into an alumina petri dish and heated at 140° C. for 2 hours using a hot plate to remove moisture. The silica powder obtained was then heated in an electric furnace at 290° C. for 1 hour to completely dry it.
• the silica powder obtained was ground in an agate mortar for 10 minutes to obtain a heat-dried powder.
• a water vapor adsorption/desorption measuring device manufactured by TA Instruments Japan, product name Q5000 SA
• the water vapor adsorption amount of the heat-dried powder was measured under the following conditions in an environment where the relative humidity changed from 10% to 90%.
• the flow rate of nitrogen gas was 200 mL/min, and the measurement temperature was 25° C.
• the heat-dried powder was dried in an electric furnace at 200° C. for 1 hour to remove adsorbed water, and 10 mg of the sample powder was weighed into a platinum container within 5 minutes and subjected to the measurement.
• a BET plot was created from the relationship between the obtained water vapor adsorption amount and relative humidity, and an approximate straight line was obtained in the relative humidity range of 0.20 to 0.35.
• the slope of the straight line, W M was taken as the water vapor adsorption weight per 1 g of the measured sample, and the specific surface area, S H2O , of the measured sample based on the water vapor adsorption method was calculated using the following formula.
• N A is Avogadro's number
• a M is the cross-sectional area occupied by one water molecule
• M H2O is the molecular weight of water. From the specific surface area S H2O based on the water vapor adsorption method measured above and the specific surface area S N2 based on the nitrogen gas adsorption method obtained in 2-1), the ratio thereof, S H2O /S N2 , was calculated.
• Example 3 Preparation of polishing composition (Example 1) Using the colloidal silica dispersion A obtained in Synthesis Example 1, each reagent and pure water were added so that the silica particles derived from colloidal silica dispersion A were 20.5 mass%, the tetrasodium salt of ethylenediaminetetraacetic acid was 0.65 mass%, tetramethylammonium hydroxide (TMAH) was 1.0 mass%, and potassium carbonate was 1.5 mass%, and the mixture was stirred for 30 minutes to obtain the polishing composition of Example 1.
• Example 2 A polishing composition of Example 2 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion B obtained in Synthesis Example 2 was used.
• Example 3 A polishing composition of Example 3 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion C obtained in Synthesis Example 3 was used.
• Example 4 A polishing composition of Example 4 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion D obtained in Synthesis Example 4 was used.
• Example 5 A polishing composition of Example 5 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion E obtained in Synthesis Example 5 was used.
• Example 6 A polishing composition of Example 6 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion F obtained in Synthesis Example 6 was used.
• Comparative Example 1 A polishing composition of Comparative Example 1 was prepared in the same manner as in Example 1, except that a colloidal silica dispersion (trade name: Snowtex XL) manufactured by Nissan Chemical Industries, Ltd. was used as the colloidal silica dispersion.
• Comparative Example 2 A polishing composition of Comparative Example 2 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion G obtained in Synthesis Example 7 was used.
• Comparative Example 3 A polishing composition of Comparative Example 3 was prepared in the same manner as in Example 1, except that a colloidal silica dispersion (product name PL-3) manufactured by Fuso Chemical Co., Ltd. was used as the colloidal silica dispersion.
• Comparative Example 4 A polishing composition of Comparative Example 4 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion H obtained in Synthesis Example 8 was used.
• Comparative Example 5 A polishing composition of Comparative Example 5 was prepared in the same manner as in Example 1, except that the colloidal silica dispersion I obtained in Synthesis Example 9 was used.
• polishing test The polishing compositions of Examples 1 to 6 and Comparative Examples 1 to 5 were each diluted 20 times by mass with pure water to obtain compositions for polishing tests.
• a polishing test was carried out under the following polishing conditions using the above polishing test composition.
• the wafer to be polished was a single crystal silicon wafer, with a diameter of 200 mm, a conductivity type of P-type, a crystal orientation of Miller index ⁇ 100>, and a resistivity of 100 ⁇ cm or less.
• the polishing test composition was supplied by a circulation method, and the liquid temperature was 23 to 25° C.
• the polishing time was 60 minutes per batch, and three batches of polishing were carried out using the same polishing pad.
• the amount of polishing liquid was 25 kg, and new polishing liquid was not replenished or pH adjusted between batches.
• Polishing machine Hamai Sangyo Co., Ltd.
• Product name Double-sided polishing machine 13BF Polishing pad: JH-RHODES Co., Ltd., product name LP-57, groove width 2 mm, groove pitch 20 mm
• Polishing load 150g/ cm2
• Rotation ratio 3.3 Number of pieces polished: 3 sets of 1 wafer/carrier were prepared, and a total of 3 pieces were polished simultaneously.
• Supply amount of polishing test composition 6.4 L/min Polishing time: 60min
• Carrier Epoxy glass carrier (thickness 0.70 mm)
• the polishing rate was calculated by measuring the thickness of the wafer before and after polishing using a laser displacement meter manufactured by Keyence Corporation (manufactured by Keyence Corporation, product name SI-F1000), subtracting the thickness of the wafer after polishing from the thickness of the wafer before polishing, and dividing the result by the polishing time of 60 min.
• the surface roughness was measured by measuring the root mean square height in a 111 ⁇ m square area in the center of the wafer using a 100x objective lens and an optical interference microscope system (trade name) BW-M7000 manufactured by Nikon Solutions Corporation.
• the polishing speed was 0.32 to 0.34 ⁇ m/min in Examples 1 to 6, and 0.32 to 0.33 ⁇ m/min in Comparative Examples 1 to 5, which showed comparable performance.
• the surface roughness was 1.09 to 1.16 nm in Examples 1 to 6, and 1.13 to 1.17 nm in Comparative Examples 1 to 5, which also showed comparable performance.
• the Rsp value of the colloidal silica dispersion used to prepare the polishing composition was within a certain range in Examples 1 to 6, and the rate of change in the average secondary particle diameter was 0 to 2%, which was a good result.
• This is thought to be because, in the silica particles based on the colloidal silica dispersion having an Rsp value of 0.07 to 0.14, there are few hydroxyl groups (OH ⁇ ) bound near the particle surface, and excessive dissolution of the silica particle surface by the hydroxyl groups is suppressed, so that aggregation of the silica particles is suppressed and the storage stability is excellent.
• the polishing composition of the present invention can be used not only as an abrasive for silicon wafers, but also as an abrasive for CMP of device wafers because of its high removal rate and storage stability.
• silica sol used in the polishing composition by using silica particles having a specific Rsp value obtained by pulse NMR, a high polishing rate can be obtained when used to polish silicon wafers, and the storage stability of the polishing composition can be improved.

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